The present invention relates to an anticatching device for automatic doors or windows, especially those of vehicles.
The doors of buses, trolleys, subways, and similar means of transportation are usually opened and closed from the driver's seat by means of a signal. To avoid accidents, safety devices are provided to prevent the passengers or their clothing or other belongings from getting caught in the closing door and to keep the door itself from getting stuck in the half-opened position.
Various types of safety devices, like light barriers parallel to the plane of closure of the door or like limit switches in the rubber that covers its edge, are known. Because such devices do not provide enough safety and because they are subject to breakdown, it has already been proposed in U.S. Pat. No. 4,376,971 to couple with the door or door mechanism, an electric signal generator that emits an electrical signal every time the door reaches a predetermined position, the signals being fed into memory elements wherein they are compared with given intervals. When anything gets caught in the door and delays its motion so that the interval between two position signals increases beyond a predetermined limit, the generator will emit a control signal to stop or reverse the motion of the door. The intervals between the detected position signals are compared with the given intervals by memory elements.
This previously proposed safety device is reliable and can be easily adapted to the opening or closing speed of a door because the predetermined intervals stored in the memory unit can be regulated. The device, however, also has drawbacks in that the memory elements must be readjusted individually for each individual door, which consumes a lot of labor during installation, and in that the speeds at which doors open and close not only differ from door to door but also depend on ambient conditions, especially temperature. If the doors are adjusted at normal room temperature, they may open at low winter temperatures so slowly that the predetermined interval is exceeded, releasing a control signal that will stop or reverse their motion.